There have been known a variety of watery materials. In terms of reuse and quality improvement thereof, a variety of types of means for treating the watery materials is under development.
For example, a sludge generated in a sewage line has generally been incinerated and the incineration ash has been buried for disposal. Incineration thereof requires a preliminary treatment in which a condensation treatment, a dewatering treatment, and drying treatment of considerable amount of fluid contained therein are appropriately combined. Therefore, the incineration thereof is difficult. Whereas a large amount of sewage sludge is discharged, there is a limitation to a ground for disposing the sewage sludge. Therefore, there is a need for technology for reusing the sewage sludge.
An example of dewatering technology is an in-oil modification process (see, for example, Patent Document 1), wherein the prospective water-containing solid is coal. In this process, a water-containing solid slurried in oil is subjected to heat treatment at a temperature of 150° C. or higher, for evaporating the aqueous component in the water-containing solid. By using a liquid oil that is not evaporated at an operating temperature as heating medium, water is selectively evaporated. Therefore, water vapor is not diluted, and a density of evaporative latent heat of water vapor is not reduced. Thus, it is assumed that evaporative latent heat of water vapor can be efficiently recovered in the in-oil modification process. Especially in coal dewatering, it is assumed that the in-oil modification process requires the least energy among all of the know approaches. However, in the in-oil modification process, separation of oil from coal (deoiling) requires centrifugal separation or heating operation at a temperature higher than 150° C. since the oil has a boiling point which is higher than that of water. Thus, the energy consumed at a deoiling step is higher than the energy consumed at dewatering step. Therefore, a full-scale commercial operation of the in-oil modification process has not been practiced yet.    Patent Document 1: Japanese Patent Application Laid-open No. 2000-290673 A